Enhanced electrochemical and dielectric properties of graphene nanoplatelet/polypyrrole nanocomposites for high-performance sustainable supercapacitors

Summary

Graphene nanoplatelet/polypyrrole (GNPLs/PPy) nanocomposites with different loadings of GNPLs (10%–50%) have been successfully prepared by a facile in situ oxidative polymerization and evaluated as advanced electrode materials for supercapacitors. Structural and morphological analyses (Fourier transform infrared [FTIR], X-ray diffraction [XRD], and Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy [SEM–EDX]) confirmed homogeneous incorporation of GNPLs into the PPy matrix, resulting in strong π-π interactions and enhanced interfacial adhesion. Dielectric permittivity explored the improvement in dielectric constant with GNPLs concentration due to interfacial polarization at the surfaces of GNPLs and PPy nanoparticles (NPs). Alternating Current (AC) conductivity spectra presented a significant enhancement in the conductivity value of the GNPLs/PPy nanocomposite compared with PPy NPs, due to simple hopping of charge carriers through the conductive GNPLs network. Electrochemical studies demonstrated a remarkable specific capacitance of 646.61 F g⁻¹ at 0.25 A g⁻¹ for the 50% GNPLs/PPy nanocomposite, with 70% capacitance retention after 1,500 cycles. These findings establish GNPLs/PPy as promising, sustainable, and cost-effective materials for next-generation high-energy-density supercapacitors.

Graphical abstract

Highlights

• •GNPLs/PPy nanocomposites were synthesized via in situ oxidative polymerization
• •Dielectric properties were directly correlated with electrochemical performance
• •50% GNPLs/PPy retained ∼70% capacitance after 1500 cycles
• •GNPLs/PPy offers a low-cost and scalable platform for supercapacitors

Electrochemistry; Applied sciences; Materials science

Introduction

The rapid growth of portable electronics and hybrid electric vehicles has intensified the global demand for efficient, durable, and cost-effective energy-storage systems.¹ Among advanced energy-storage technologies, supercapacitors bridge the gap between conventional capacitors and rechargeable batteries by offering high power density, rapid charge-discharge capability, and long cycling life. The development of electrode materials that are metal-free, scalable, and fabricated through low-energy processes is essential for advancing environmentally responsible energy technologies.² In this context, polymer-carbon nanocomposites provide an attractive pathway due to their relatively low material cost, commercial availability, eco-friendliness, and compatibility with processing routes. The utilization of conducting polymers and carbon-based conductive fillers promotes the fabrication of high-performance electrode materials, ultimately supporting the advancement of resourceful, effective, and easily accessible energy-storage systems.^3,4,5

Furthermore, supercapacitors are advanced technological boosting agents for future electrochemical energy conversion and storage systems.⁶ Although supercapacitors are efficient electrochemical energy-storage devices, there are still several drawbacks in their electrochemical performance, stability, and cost. Hence, higher energy-density devices with high supercapacitive characteristics can be fabricated by materials that can undergo faradaic charge-transfer reactions; however, such nanomaterials generally exhibit poor stability and lower energy and power densities.⁷

To achieve this goal, different conducting polymers and carbonaceous materials are extensively studied as an electrode active material for the application of supercapacitors. Among various conductive electroactive polymers, polypyrrole (PPy) is one of the most proficient materials owing to its easy synthesis method, higher capacitance, and improved chemical and thermal stability.^8,9 In spite of the higher capacitance of PPy, its use in many applications is limited because of its poor mechanical strength and low charge-discharge efficiency.¹⁰ Thus, greater capacitance, high conductivity, and good mechanical stability in supercapacitor devices have been revealed by using the carbon base polymer nanocomposites.^11,12 However, the high cost of carbon nanotubes and their greater double-layer capacitance of 80 F g⁻¹ have attracted scientists to explore other innovative carbonaceous nanomaterials.¹³

Integrating PPy with carbon nanostructures such as graphene nanoplatelets (GNPLs) provides an effective strategy to overcome these drawbacks. GNPLs have sp²-linked carbon atoms arranged in a two-dimensional hexagonal network and are the center of attention due to their excellent mechanical stability, higher specific surface area, and greater electrical conductivity.^13,14 Recently, graphene-polymer nanocomposites have been extensively investigated for supercapacitors with significant specific capacitance. Zhang et al.¹⁵ synthesized graphene-PPy by chemical polymerization of pyrrole monomer with graphene nanosheets and accomplished 482 F/g specific capacitance at 0.5 A/g. Liu et al.¹⁶ also synthesized the graphene-based PPy composite by polymerizing pyrrole in graphene oxide (GO) solution, subsequently reducing through ethylene glycol (EG). The prepared composites exhibited better charge-discharge capability, higher rate performance, and larger specific capacitance. Moreover, Zhang et al. also fabricated the ternary graphene/PPy/carbon nanotube (GN/PPy/CNT) composite by the chemical polymerization technique.¹⁷ The graphene-PPy-CNT materials having an 8:1 ratio of GN:CNT demonstrate a high (112 m² g⁻¹) surface area and a higher specific capacitance, i.e., 361 F/g at 0.2 A/g current density than pure PPy, CNT/PPy, and GN/PPy binary composites that have 176, 253, and 265 F g⁻¹ specific capacitance, respectively. Similarly, Xu et al.¹⁸ prepared a melamine sponge-modified graphene/PPy (G-PPy-G-MS) electrode by coating the PPy and reduced GO (rGO) on the surface of a melamine sponge. The G-PPy-G-MS composite exhibits a higher specific capacitance of 464.10 F g⁻¹ at 0.5 A g⁻¹ with superior rate performance.

Different studies revealed that graphene-PPy (G/PPy) composites are used as electrode materials for supercapacitors, mainly focusing on the increased specific capacitance through redox activity optimization and structural framework. However, most of the studies used rGO, graphene papers, GO, or other complex ternary geometries, but their performance is merely limited to electrochemical measurements.^19,20,21

In contrast, GNPLs offer higher electrical conductivity, structural stability, and scalable processability, which are comparatively underexplored with the integration of PPy nanoparticles (PPy NPs), progressively produced by a controlled in situ polymerization technique, with a systematic assessment of both dielectric and supercapacitor performance. Particularly, the role of GNPLs content in AC conductivity, interfacial polarization, and charge-transfer kinetics has not been comprehensively interconnected with electrochemical properties. Therefore, the idea was to establish a quantitative connection between dielectric polarization mechanisms and electrochemical charge storage for better understanding of the structural property relationship in the carbon-polymer hybrid electrode system. Currently, we focus on a composition-dependent study (10–50 wt % GNPLs) that highlights the structural/morphological features, dielectric behavior, and electrochemical properties, providing a better view of multifunctional polymer-carbon nanocomposites.

Results and discussion

Characterization

The X-ray diffraction (XRD) patterns of pristine PPy NPs and GNPLs/PPy nanocomposites (10%, 30%, and 50%) are presented in Figure 1. The broad feature of pristine PPy reflects its amorphous polymeric nature, which is typical for PPy chains lacking a long-range order.²² The XRD pattern of pristine PPy exhibits a broad diffraction halo centered at approximately 2θ ≈ 20–25°, which is characteristic of the predominantly amorphous structure of PPy. Unlike crystalline solids, conducting polymers like PPy do not possess a wide periodic arrangement because of irregular ordering and coiled conformation of polymer chains formed during the process of oxidative polymerization. Subsequently, X-ray scattering mostly arises from π-π stacking interactions and short-range ordering among adjacent PPy units, as a result of which it generates a diffuse broader peak rather than ordered crystalline lattices. Recently, the amorphous properties of PPy have been discussed in literature in which a wide peak around 2θ ≈ 19–25° is the indication of disordered polymeric chains and partial/short structural periodicity in the polymer matrix.^23,24

Figure 1.

XRD spectra of four different electrodes

(A) Pristine PPy NPs.

(B) 10% GNPLs/PPy.

(C) 30% GNPLs/PPy.

(D) 50% GNPLs/PPy nanocomposites.

Therefore, the presence of non-crystalline geometry confirms the amorphous nature of PPy polymeric backbones having a shorter molecular arrangement, which is the characteristic feature of conducting polymers formed through a chemical oxidative polymerization reaction (Figure 1).

After incorporation of GNPLs, a distinct peak appears at 2θ ≈ 26.8°, corresponding to the (002) plane of graphitic carbon, confirming the presence of graphene layers within the polymer matrix. This feature demonstrates successful intercalation of GNPLs and strong π-π interactions between graphene sheets and PPy backbones, leading to enhanced structural ordering.^25,26,27

Scanning electron microscopy (SEM) micrographs (Figure 2A) reveal spherical PPy NPs with an average diameter of ∼50 nm, uniformly coated over GNPLs surfaces in the composites. The surface topography of 10% GNPLs/PPy, 30% GNPLs/PPy, and 50% GNPLs/PPy nanocomposites reveals the bi-phase temperament of nanomaterials as presented in Figures 2B–2D, which highlights that graphene strongly affects the morphology of PPy during the process of polymerization. At higher GNPLs contents, the PPy NPs anchor densely along the graphene sheets, forming a conductive interconnected network. The results confirm the successful formation of nanocomposites as we reported in our previous paper.²⁸ The surface morphology thus supports efficient electron transport and ion accessibility (Figure 2).

Figure 2.

SEM images of four different electrodes

(A) Pristine PPy NPs.

(B) 10% GNPLs/PPy.

(C) 30% GNPLs/PPy.

(D) 50% GNPLs/PPy nanocomposites.

Energy-dispersive x-ray spectroscopy (EDX) spectra (Figures 3A–3D) confirm the presence of carbon and nitrogen as dominant elements in the nanomaterials. Carbon indicates the presence of GNPLs and pyrrole, while nitrogen is the main structural constituent of the pyrrole monomer, which confirmed that PPy is covalently bonded with GNPLs in nanocomposites.²⁹ EDX results verify covalent incorporation of PPy onto GNPLs through polymerization of the pyrrole monomer on graphene surfaces³⁰ (Figure 3).

Figure 3.

EDX spectra of four different electrodes

(A) Pristine PPy NPs.

(B) 10% GNPLs/PPy.

(C) 30% GNPLs/PPy.

(D) 50% GNPLs/PPy nanocomposites.

Infrared (IR) plots for pristine PPy NPs and GNPLs/PPy (10%, 30%, and 50%) nanocomposites are presented in Figure 4. The IR plot of pristine PPy NPs shows that a band emerging at 1,180 cm^−⁠1 is associated with the S=O aromatic ring of PPy in the doped condition, while the bands near 1,548 and 1,305 cm^−⁠1 symbolize C=C and C–N, respectively, which are associated with stretching vibrations of pristine PPy NPs and correspond to the polaron and bipolaron structures of oxidized PPy. These bands also appeared in the spectra of 10% GNPLs/PPy, 30% GNPLs/PPy, and 50% GNPLs/PPy nanocomposites. In GNPLs/PPy nanocomposites, bands at 1,035 and 1,534 cm^−⁠1 are attributable to the bipolaron state of PPy, which indicate strong interfacial interactions between PPy chains and GNPLs. These changes confirm that polymerization occurred successfully on the graphene surface, forming a hybrid network with improved electrical pathways. Moreover, some bands shift slightly, which highlight the inclusion of PPy NPs at the GNPLs interface in the GNPLs/PPy nanocomposites.³¹ With increasing GNPLs loading, slight variations in peak intensity are noticed, which indicates interfacial interactions between GNPLs and the PPy matrix. These interactions influence the electronic structure and contribute to enhanced electrical conductivity and electrochemical properties of the nanocomposites. The IR spectra designate the successful preparation of GNPLs/PPy nanocomposites as published in our previous paper²⁸ (Figure 4).

Figure 4.

FTIR spectra of four different electrodes

(A) Pristine PPy NPs.

(B) 10% GNPLs/PPy.

(C) 30% GNPLs/PPy.

(D) 50% GNPLs/PPy nanocomposites. The inset shows a magnified view of the 1,700–600 cm⁻¹ region for clearer visualization of the characteristic vibrational bands.

The dielectric properties of pristine PPy and GNPLs/PPy composites were evaluated over the frequency range of 50 Hz–20 MHz. Figures 5A–5C show the frequency dependence of real permittivity (ε′), imaginary permittivity (ε″), and tan δ. Results confirmed that the real and imaginary permittivity of pristine PPy NPs is independent of frequency, while in GNPLs/PPy nanocomposites (10%, 30% and 50%) it reduced with the increase of frequency, which corresponds to the declining ability of dipoles in the nanocomposites to retain the fast in-phase oscillating motion of the incident electromagnetic (EM) wave. At low frequency, the dipoles connect with the electric field before changing its direction; as a result, the dielectric constant elevates, while at higher frequency, dipoles cannot change the electric vector quickly, and the dielectric constant reduces. In addition, results also show that the dielectric loss (ε″) and dielectric constant (ε') of the nanocomposite increase with the addition of GNPLs, as shown in Figures 5A and 5B. Besides, the permittivity of the composites increases with increasing GNPLs concentration, which is due to interfacial polarization, as the space charges increase, leading to an increase in permittivity. Thus, the increase in ε′ with GNPLs loading demonstrates improved interfacial polarization at the GNPLs/PPy interface and confirms enhanced charge storage ability. The polarons or bipolarons (doping-induced localized charges) on the pristine PPy NPs generate superior polarization effects. Moreover, in PPy, the formation of space charge, as a result of the conductivity difference between the electrically insulating amorphous matrix and the highly conducting/ordered (crystalline) islands, contributes to interfacial polarization.

Figure 5.

Frequency-dependent dielectric behavior of pristine PPy nanoparticles and GNPLs/PPy nanocomposites

(A) Real permittivity.

(B) Imaginary permittivity.

(C) Loss tangent (tan δ).

(D) AC conductivity.

Figure 5C shows the dielectric loss (tan δ) plots of pristine PPy NPs and GNPLs/PPy (10%–50%) nanocomposites at room temperature over a frequency range of 50 Hz to 20 MHz. Results highlighted that as the GNPLs content increases in the nanocomposites, the dielectric loss increases with decreasing frequency, which is attributed to the good compatibility between GNPLs and PPy NPs and interfacial polarization relaxation in the nanocomposites, which arises as a result of π-π stacking and the large surface area of GNPLs. Such GNPL-based nanocomposites with low dielectric loss and greater dielectric constant are promising agents for different functional applications i.e., gate dielectrics, embedded capacitors, and high charge-storage capacitors. So, GNPLs/PPy nanocomposites (10%, 30%, and 50%) are best dielectric candidates, which can be extensively utilized for high-frequency and embedded capacitor applications.^32,33 (Figure 5).

The alternating current (AC) conductivity (σ_ac) of the nanocomposites was calculated using the relation

$$\mathrm{\sigma }\text{ac}=2\mathrm{\pi }\mathrm{f}\mathrm{\epsilon }0{\mathrm{\epsilon }}^{″}\text{,}$$

where f is the applied frequency, ε₀ is the permittivity of free space, and ε′′ is the imaginary part of the dielectric permittivity. Likewise, the increase in dielectric loss and AC conductivity with GNPLs content (Figure 5D) reflects facilitated charge-carrier hopping through the continuous graphene network. Figure 5D also shows that AC conductivity for pristine PPy NPs and for low-concentration nanocomposites, i.e., 10% loading of GNPLs in PPy NPs, oppose flow of charge carriers, thus decreasing the AC conductivity except for 30% and 50% nanocomposites. For these two nanocomposites, conductivity is increased, which is probably due to the increase in localized hopping sites for charge carriers and the high surface area of GNPLs. Thus, these results signified that the addition of an appropriate amount of GNPLs improved the AC conductivity. The AC conductivity has been significantly enhanced when higher amounts of GNPLs i.e., 30% and 50%, have been anchored to the PPy NP matrix. Among all compositions, the 50% GNPLs/PPy composite exhibits the highest dielectric constant and AC conductivity, attributed to its dense percolation of conductive graphene sheets. These results establish that appropriate GNPLs incorporation significantly enhances both dielectric response and electrical conductivity, providing a strong foundation for electrochemical performance improvement.

Cyclic voltammetric (CV) analysis was performed for the evaluation of electrochemical characteristics of pristine PPy NPs and GNPLs/PPy (10%, 30%, and 50%) nanocomposites in an aqueous 1 M H₂SO₄ electrolyte using a three-electrode electrochemical configuration (Figures 6A and 6B), while the CV results are shown in Figures 7A–7C. The potential windows were optimized for each technique to ensure electrochemical stability and reliable performance, avoiding overoxidation and electrolyte decomposition. Figure 7A illustrates that the as-prepared nanomaterials display quasi-rectangular shapes with noticeable redox peaks, confirming pseudocapacitive behavior derived from PPy redox activity. The current response increases. The cathodic peak current (Ipc) is positioned at about 0.36 and 0.85 mA, and the anodic peak current (Ipa) is located at 0.10 and 0.374 V at 50 mv/s scan rate, as can be seen in Figure 7A. The visible oxidation-reduction peaks in the CV curves can be attributed to the direct transformation of electrons in PPy and graphene. This difference in redox peaks is attributable to the higher surface area and larger electrical conductance of GNPLs and PPy, which can improve electron transfer. The redox process on the GNPLs/PPy surface is purely diffusion controlled in which electroactive species impulsively move from higher to lower concentration gradients.³⁴ To further support the electrochemical behavior, cyclic voltammetry at a lower scan rate (10 mV s⁻¹) was performed, and the results are presented in Figure S1. The observed redox features and current response are consistent with the trends discussed at higher scan rates, confirming the improved charge-storage behavior of GNPLs/PPy nanocomposites.

Figure 6.

Electrode preparation and three-electrode electrochemical cell configuration for GNPLs/PPy nanocomposite characterization

(A and B) Preparation of the working electrode (WE) with nanomaterial coating deposited on a silver plate current collector. (B) The three-electrode electrochemical cell showing the WE, reference electrode (RE), and counter electrode (CE) connected to the electrochemical workstation.

Figure 7.

Electrochemical properties of pristine PPy NPs and GNPLs/PPy nanocomposites in a three-electrode configuration

(A) Comparative cyclic voltammogram at a scan rate of 50 mV/s.

(B) Cyclic voltammograms of the 50% GNPLs/PPy nanocomposite at scan rates of 10–200 mV/s (from inside to outside).

(C) Specific capacitance ability.

Moreover, the area of CV spectra is related to capacitance, which is contributed by redox peaks. As shown in Figure 7A, the 50% GNPLs/PPy nanocomposite displays a significantly higher area than pristine PPy, 10% GNPLs/PPy, and 30% GNPLs/PPy nanocomposites, suggesting a higher capacitance of the nanomaterial, and it is also due to the synergistic effect of highly conductive GNPLs and PPy NPs. Perhaps, the GNPLs can possibly provide a platform/skeleton for the polymerization of pyrrole, which enhances the electrical conductivity and strength of nanocomposites. Contrarily, inclusion of GNPLs in PPy NPs hampers the stacking of GNPLs and increases the interlayer spaces of graphene, which leads to the high pseudocapacitive behavior of the electrode materials.³⁵

The electrochemical performance of the composites is due to the pseudocapacitive behavior arising from rapid and reversible Faradaic redox reactions taking place at the surface of electrode-electrolyte surface. Explicitly, PPy undergoes reversible doping/dedoping processes during charge-discharge cycles,³⁶ which can be represented as

$$\text{PP}{\mathrm{y}}^0+\mathrm{n}{\mathrm{A}}^{-}\leftrightarrow \text{PP}{\mathrm{y}}^{\mathrm{n}+}{\left({\mathrm{A}}^{-}\right)}_{\mathrm{n}}+\mathrm{n}{\mathrm{e}}^{-}\text{,}$$

where A⁻ represents electrolyte anions participating in charge compensation.

During the process of oxidation, PPy carries a positive charge and integrates anions from the electrolyte solution, while during the process of reduction, these anions are released from the solution, resulting in reversible charge storage. The GNPLs incorporation further improves the electrochemical properties by offering a highly conductive network which increases the electron transport pathways, and providing additional electroactive surface area. This leads to enhanced charge-transfer kinetics and better use of redox-active sites. Furthermore, the coordination among electric double-layer capacitance from graphene and pseudocapacitance from PPy contributes to the inclusively enhanced performance. The synergistic amalgamation of pseudocapacitance from PPy and double-layer capacitance from graphene results in enhanced electrochemical performance, consistent with previous reports.³⁷

At scan rates between 10 and 200 mV s⁻¹ (Figure 7B), the 50% GNPLs/PPy electrode maintains a nearly symmetrical profile, demonstrating good rate capability. The increase of current with scan rate indicates that nanocomposites exhibit good capacitive properties with rapid oxidation and reduction reaction on the alterations of current. Additionally, in the process of quick electrochemical reactions, the electrolyte ions cannot reach the electrode surface, which results in a decrease in redox peaks intensity with increasing scan rate (Figure 7).

The specific capacitance from CV curves at various scan rates, as shown in Figure 4C, was calculated using Equation 1³⁸:

$${\mathrm{C}}_{\text{sp}}=\mathrm{I}/2\Delta \text{VmS,}$$ (Equation 1)

where I represents the integrated area from the CV curve, S is the scan rate, m represents the mass of coated material, and ΔV is the applied potential window for electrode material. The Csp values (Figure 7C) of the GNPLs/PPy supercapacitors reduce with increasing scan rates from 5 to 200 mV/s, which is due to the effect of ionic diffusion in the electrode and at the electrode-electrolyte interface. In short, specific capacitance values decrease with increasing scan rate because of restricted ion diffusion at faster potential sweeps. At 5 mV s⁻¹, the 50% GNPLs/PPy nanocomposite delivers 1,282.5 F/g, which is almost three times higher than pristine PPy (444 F g⁻¹), which could be attributed to the synergistic effect of GNPLs and PPy NPs. The results are supported by SEM-EDX, galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) data^39,40 (Figure 8).

Figure 8.

Capacitance retention ratio of 50% GNPLs/PPy measured at a scan rate of 50 mV/s

Cyclic stability tests (Figure 8) show that the 50% GNPLs/PPy electrode retains 70% of its initial capacitance after 1,500 cycles at 50 mV s⁻¹. The excellent stability results from mechanical reinforcement provided by GNPLs and strong interfacial adhesion, which mitigate structural degradation during repeated redox cycling. Besides, the better cyclic stability is also due to stronger intermolecular forces between pyrrole and GNPLs and lower surface energy and surface tension of GNPLs/PPy before polymerization of pyrrole monomers.⁴¹

The cycling durability observed in this study is consistent with the well-documented behavior of conducting polymer-based pseudocapacitive electrodes. PPy inherently undergoes volumetric expansion and contraction during repeated redox processes, which can gradually induce structural stress and capacitance decay over extended cycling, particularly in acidic electrolytes. In many reported graphene-PPy and PPy-based systems evaluated in three-electrode configurations, stability tests are commonly presented within the range of 1,000–2,000 cycles for material-level assessment.^42,43,44,45 Therefore, the 1,500-cycle evaluation performed here provides a representative and meaningful measure of electrochemical durability while enabling analysis of the dielectric-electrochemical coupling mechanism. Further enhancement of ultra-long-term cycling stability will be addressed in future device-oriented optimization studies. A comparative summary of reported cycling stability for similar PPy-based systems is provided in Table S1 (Figure 9).

Figure 9.

Electrochemical performance of pristine PPy NPs and GNPLs/PPy nanocomposite supercapacitor in a three-electrode system

(A) GCD curves at current density of 0.25 A/g.

(B) Comparison of specific capacitance at different current densities.

(C) Ragone plot of pristine PPy NPs and GNPLs/PPy nanocomposites.

The GCD analyses are performed to study the electrochemical capacitance of the sample electrodes. Figure 9A illustrates the GCD spectra of pristine PPy and GNPLs/PPy (10%, 30% and 50%) nanocomposites at different charge and discharge current densities. GCD curves further verify the pseudocapacitive nature of the electrodes, showing non-linear, quasi-triangular profiles. The 50% GNPLs/PPy electrode exhibits the longest discharge time, confirming its superior energy-storage capacity. The specific capacitance of the electrode using galvanostatic data is calculated by Equation 2:

$${\mathrm{C}}_{\text{sp}}=\frac{\mathrm{I}\times \Delta t}{\mathrm{m}\times \Delta V}\text{,}$$ (Equation 2)

where ΔV is the potential window, and I, m, and Δt represent current, the mass of active material, and discharge time, respectively. The Csp of 50% GNPLs/PPy is greater than pristine PPy and 10% GNPLs/PPy and 30% GNPLs/PPy nanocomposites at the same current density, which are prominent in the Csp plots (Figure 9B). The 50% GNPLs/PPy exhibited the highest Csp of 646.61 F g⁻¹ at a 0.25 A g⁻¹ current density, which is greater than that of pristine PPy, i.e., 280 F g⁻¹, outperforming many similar composites reported previously, as summarized in Table 1. The enhanced capacitance of the 50% GNPLs/PPy nanocomposite is chiefly attributed to its better conductivity, smaller particle size, and higher surface area, which makes the diffusion of ions easy and augments the utilization of nanomaterials as an electrode for ultracapacitor applications.⁷¹ The results demonstrate that the capacitance of the nanomaterials reduces as the current density increases. At lesser current density, higher consumption of electroactive materials helps to precede the process of charge/discharge, whereas at greater current density, the ionic transmission through internal active sites could not be completed, and as a result, the capacitance of the electrode material diminishes. In addition, Table 1 illustrates the comparison of the specific capacitance of this work with other reported studies.

Table 1.

Comparison of the electrochemical performance of graphene-polypyrrole-based composite electrodes reported in the literature with the GNPLs/PPy nanocomposites developed in this study

Active material	Electrolyte	Specific capacitance	Current density/scan rate	Reference
Polypyrrole/graphene/melamine composite foam	6 M KOH	422.6 F g−1	0.5 A g−1	Qu et al.46
PET/MOF-6/rGO/PPy	1 M H2SO4	510 mFcm−2	1 mV s−1	Barakzehi et al.47
Graphene/polypyrrole Composites	1 M H2SO4	424 F g−1	1 A g−1	Chang et al.48
Graphene paper-polypyrrole composite (GrP-PPy)	0.5 M H2SO4	462.8 F g−1	1 mV s−1	Wang et al.49
Polypyrrole/reduced graphene oxide hybrids	1 M H2SO4	198 F g−1	20 A g−1	Moyseowicz et al.50
Graphene/polypyrrole hydrogel	H3PO4-PVA	363 F cm−3	1.0 mA cm−3	Wu et al.51
Graphene/polypyrrole composite	1 M H2SO4	482 F g−1	0.5 A g−1	Zhang et al.52
Holey graphene/polypyrrole hybrid aerogels (HGPAs)	1 M KOH	418 F g−1	0.5 A g−1	He et al.53
G/PPy/MnOx/Cu(OH)2	6 M KOH	370 F g−1	10 mV s−1	Miankushki et al.54
Nanoclay-based ternary graphene/polypyrrole	1 M KCl	347 F g−1	10 mV s−1	Zhang et al.55
Reduced graphene oxide/polypyrrole composites	PVA-H2SO4	147.9 F cm−3	5 A cm−3	Liu et al.56
Graphene-polypyrrole (G/PPy)	1 M H2SO4	256 F g−1	0.5 mA/g	Punya et al.57
Polypyrrole@TEMPO-oxidized bacterial cellulose/reduced graphene oxide macrofibers	PVA/H2SO4	391 F g−1	0.5 A g−1	Sheng et al.58
Polypyrrole/reduced graphene oxide-coated fabric	2.0 M NaCl	336 F g−1	0.6 mA/cm2	Xu et al.59
Graphene/Co3O4/polypyrrole ternary nanocomposite	6 M KOH	422 F g−1	10 mV s−1	Khalaj et al.60
N-doped graphene/polypyrrole (NG-PPy)	6 M KOH	393.67 F g−1	2 mV s−1	Laia et al.61
Graphene/polypyrrole/Cu(OH)2	6 M KOH	311 F g−1	10 mV s−1	Miankushki et al.62
Graphene nanosheets/PPy nanowire	1 M NaCl	165 F g−1	1 A g−1	Biswas et al.63
Graphene/PPy composite film	1 M H2SO4	335 F g−1	1 A g−1	Feng et al.64
Graphene/polypyrrole intercalating nanocomposites	1 M H2SO4	318.6 F g−1	0.45 A g−1	Liu et al.65
Hierarchical graphene/PPy nanosheets	1 M H2SO4	318.6 F g−1	2 mV s−1	Xu et al.66
PPy/MnFe2O4/rGO	1 M Na2SO4	147 F g−1	10 mV s−1	Thu et al.67
PPy/GO/MWCNT	1 M Na2SO4	358.6 F g−1	100 mV s−1	Abdah et al.68
PPy/PANI coaxial nanotube hybrid in rGO	1 M H2SO4	542 F g−1	1 A g−1	Zhang et al.69
Polypyrrole-CNT-graphene	0.5 M H2SO4	453 F g−1	5 mV s−1	Aphale et al.70
Polypyrrole-CNT-graphene	0.5 M H2SO4	453 F g−1	5 mV s−1	Aphale et al.70
GNPLs/PPy (this work)	1 M H2SO4	1,095 F g-1	5 mV s−1	this study
		646.61 F g-1	0.25 A g−1

Specific capacitance values are reported as provided in the respective references and were obtained under different testing conditions (electrolyte, current density, scan rate, and electrode configuration). The table is intended to provide a qualitative performance comparison. Bold values indicate the electrochemical performance parameters reported in the present work.

Specific energy and specific density are the most significant factors used to measure the actual capacity of the nanocomposites. At different current densities, the energy density and power density are estimated using the charge/discharge plots by (Equation 3), (Equation 4).⁴⁷

$$E=\frac{1}{2}{C}_{sp}{V}^2\text{,}$$ (Equation 3)

where Csp represents the specific capacitance anticipated from charge/discharge plots, and V represents the potential window. The power density (P) is also assessed from GCD curves according to Equation 4⁷²:

$$P=\frac{E}{t}\text{,}$$ (Equation 4)

where E is the energy density and t is the discharge time in seconds obtained from charge/discharge spectra. The specific energy and specific power of pristine PPy and GNPLs/PPy, (10%, 30%, and 50%) are marked in the Ragone plot (Figure 9C). The Ragone plot demonstrates that the 50% GNPLs/PPy electrode achieves an energy density of 0.1839 Wh kg⁻¹ at a power density of 13.16 W kg⁻¹. The energy density acquired in this study (0.1839 Wh kg⁻¹ at 13.16 W kg⁻¹) appears lower compared to reported values for optimized graphene-based supercapacitor devices. However, it is important to consider the measurement configuration. Recent literature has highlighted that energy density mainly depends on the testing configuration, operating voltage, and electrolyte system. Generally, higher energy densities are achieved in fully assembled two-electrode or hybrid device systems, where the voltage window and electrode balancing are optimized. In contrast, three-electrode systems, as used in the current project, are designed to measure intrinsic material properties and usually give lower energy density values because of inadequate operating voltage. Hence, the attained energy density is consistent with previously reported material-level performances of graphene-polymer systems under similar conditions. Importantly, the observed electrochemical performance, including capacitance behavior, conductivity enhancement, and charge-transfer characteristics, reveals the usefulness of the GNPLs/PPy nanocomposite design and its potential for further device-level optimization.⁷³

Although some previously reported graphene-PPy systems exhibit comparable specific capacitance values under certain testing conditions, those studies primarily focus on electrochemical performance optimization. In contrast, the present work uniquely integrates dielectric analysis with electrochemical evaluation, enabling a deeper understanding of interfacial polarization effects and conductive network formation in GNPLs/PPy systems. Therefore, the contribution of this study lies not only in competitive capacitance performance but also in establishing a multifunctional structure-property framework.

Electrochemical impedance is one of the basic fundamental electro-analytical methods analogous to the galvanostatic analysis, used to evaluate the charge-transport activities of the electrode-electrolyte system on the basis of frequency. Figures 10A and 10B demonstrate the Nyquist diagram of pristine PPy and GNPLs/PPy (10%, 30%, and 50%) in 1 M H₂SO₄ solution. The experiments were carried out at open-circuit potentials over a frequency range of 20 kHz to 0.1 Hz (Figure 10).

Figure 10.

Electrochemical impedance analysis of pristine PPy NPs and GNPLs/PPy nanocomposites

(A) Nyquist plots of pristine PPy and GNPLs/PPy nanocomposites.

(B) Magnified view of the high-frequency region of the Nyquist plots.

(C) Equivalent circuit model used to fit the electrochemical impedance spectroscopy (EIS) data.

The Nyquist plots (Figure 10) for GNPLs/PPy (10%, 30%, and 50%) comprise a small arc in the higher frequency region, which is associated with the faradaic reaction that takes place on the electrode-electrolyte surface due to the limiting steps of electron transformation, characteristic of pseudocapacitive electrodes. In addition, the diameter of the arc indicates the faradaic charge-transfer resistance (Rct). Assessments of the impedance spectra are completed by fitting the experimental EIS plots to an equivalent electrical circuit model.⁷⁴ (Figure 11).

Figure 11.

Charge-transfer resistance of GNPLs/PPy nanocomposites with different GNPLs loadings obtained from electrochemical impedance spectroscopy

A progressive decrease in Rct with increasing GNPLs content indicates improved charge-transfer kinetics and electrical conductivity.

The suitable circuit fitting of the as-prepared nanomaterials is presented in Figure 10C. The calculated Rct values for pristine PPy, 10% GNPLs/PPy, 30% GNPLs/PPy, and 50% GNPLs/PPy are 2.8, 2.5, 2.0, and 1.8 Ω, respectively. These data highlight that 50% GNPLs/PPy has the lowest Rct value compared to other active materials, identifying faster electron transport between the electrolyte and electrode material as a result of π-π interaction and the doping process between GNPLs and PPy NPs, which allows greater accessibility of the electrolyte to the electrode surface by limiting the transmission of ions.⁷⁵ This small Rs designates the higher conductance with improved capacity of 50% GNPLs/PPy.

Figure 11 and Table 2 summarize that the decrease in Rct with increasing GNPLs content confirms improved interfacial electron transport through π-π stacking and the formation of conductive pathways. In Table 2 bold value indicate the good electrochemical performance parameter shown by 50% (GNPLs/PPy) nanocomposite. Furthermore, the perpendicular line in the low-frequency region ascribed to the lesser Warburg resistance signifies better capacitance with low diffusion impedance of the electroactive materials. The slope at 45° in the Nyquist diagram (Figure 10B) specifies the Warburg resistance (W) of electroactive nanomaterials, resulting from ion transport/diffusion in the electrolyte on the basis of frequency.^76,77 The steep low-frequency line signifies efficient ion diffusion and capacitive behavior. The EIS results corroborate the superior electrical conductivity and interfacial kinetics of the GNPLs-rich composite (Table 2).

Table 2.

Quantify EIS of GNPL/PPy nanocomposites

Sample	Rct (Ω)	Remarks
Pristine PPy	2.8	highest charge-transfer resistance, lowest conductivity
10% GNPLs/PPy	2.5	improved conductivity and charge transfer
30% GNPLs/PPy	2.2	faster charge transfer, lower Rct
50% GNPLs/PPy	1.8	best conductivity and lowest charge-transfer resistance

Bold values indicate the superior electrochemical performance exhibited by the 50 wt% GNPLs/PPy nanocomposite.

A clear composition-dependent correlation appears among the electrochemical performance and dielectric polarization in GNPLs/PPy nanocomposites. As the GNPLs content increases, the interfacial polarization enhances, and the development of a percolative conductive network instantaneously improves dielectric permittivity, charge-transfer kinetics, and AC conductivity. This enhanced electrical pathway decreases Rct and facilitates ion diffusion efficiently at the electrode-electrolyte surface, eventually giving a higher value of specific capacitance. The 50% GNPLs composition signifies the optimal balance among the conductive network and the active contribution of polymer matrices. This dual-functional behavior reveals that dielectric properties can act as a predictive tool for the optimization of polymer-carbon hybrid electrodes.

Overall, the EIS results show that integration of GNPLs enhances the electrochemical charge-transfer properties of the PPy matrix. The progressive reduction in Rct from 2.8 Ω for pure PPy to 1.8 Ω for 50% GNPLs/PPy nanocomposite indicates the development of an efficient conductive network that assists fast electron transport at the electrode-electrolyte surface. Furthermore, the sharper low-frequency slope observed in the Nyquist plots designates enhanced ion diffusion in the electrode materials. These properties indicate the better electrochemical performance and higher specific capacitance of GNPLs-rich nanocomposites.

Ultimately, innovations in such nanocomposite materials serve as vital enablers for the global transition toward affordable and reliable energy technologies, thereby directly supporting the objectives of developmental goals on clean and sustainable energy.

Dielectric-electrochemical correlation

Maxwell-Wagner interfacial polarization plays a key role in explaining the relationship between dielectric polarization and electrochemical performance in GNPLs/PPy nanocomposites. The incorporation of highly conductive GNPLs within the semiconducting PPy matrix promotes charge accumulation at the interfaces, resulting in enhanced interfacial polarization. This phenomenon increases dielectric permittivity while simultaneously facilitating efficient electron transport pathways within the composite structure. Consequently, the structural features responsible for enhanced dielectric polarization also contribute to reduced Rct and improved electrochemical capacitance (Figure 12).

Figure 12.

Correlation between charge-transfer resistance and specific capacitance of GNPLs/PPy nanocomposites measured at a current density of 0.25 A g⁻¹

The inverse relationship indicates that reduced interfacial charge-transfer resistance enhances electrochemical charge-storage performance.

This relation is further illustrated in Figure 12, which gives a correlation plot between Rct and specific capacitance, clearly indicating that increased GNPLs loading in the nanocomposites results in decreasing Rct, which leads to an improvement in capacitance. A quantitative correlation is noted among electrochemical performance and dielectric polarization behavior of GNPLs/PPy nanocomposites. With increasing GNPLs content, both AC conductivity and dielectric permittivity increase, which demonstrates high interfacial polarization and enhanced electrical pathways in the nanomaterial framework.

Similarly, the impedance study exposes a progressive reduction in Rct from 2.8 Ω for pristine PPy to 1.8 Ω for the 50% GNPLs/PPy nanocomposite, which confirms higher charge-transfer kinetics at the electrode-electrolyte interface. Furthermore, the specific capacitance examined from GCD measurements increases from 280 F g⁻¹ to 646.61 F g⁻¹, representing increased charge storage capacity. This inverse correlation between Rct and Csp, together with the simultaneous increase in dielectric permittivity and AC conductivity, confirms that the establishment of a conductive GNPLs percolation network improves both dielectric polarization and electrochemical charge transport. These outcomes show better coherence between dielectric behavior and electrochemical properties in carbon-polymer hybrid nanocomposites.

In summary, as advanced energy-storage materials, the GNPLs/PPy nanocomposites developed in this study directly contribute to the achievement of Sustainable Development Goal (SDG) 7 (Affordable and Clean Energy), as the GNPLs/PPy nanocomposites developed in this study offer a metal-free, low-cost, and scalable electrode platform fabricated through a simple aqueous polymerization process. These features, combined with improved electrochemical performance, support the development of more accessible and environmentally responsible energy-storage technologies. The GNPLs/PPy (10%, 30%, and 50%) nanocomposites were successfully synthesized through a simple in situ oxidative polymerization technique and evaluated as potential supercapacitor electrode materials. The incorporation of conductive GNPLs within the PPy matrix generated a highly interconnected network that enhanced charge transport, dielectric polarization, and mechanical stability.

Structural and dielectric analyses confirmed uniform GNPLs dispersion and strong π-π interactions with the PPy chains, leading to higher permittivity and conductivity. AC conductivity spectra presented a significant enhancement in the conductivity value of the 50% GNPLs/PPy nanocomposite as compared to pristine PPy NPs, due to simple hopping of charge carriers through the conductive GNPLs network, which commercially makes it a promising candidate as a flexible dielectric material for high-frequency supercapacitors. Electrochemical tests demonstrated that the 50% GNPLs/PPy nanocomposite achieved the highest specific capacitance of 646.61 F g⁻¹ at 0.25 A g⁻¹, an energy density of 0.1839 Wh kg⁻¹ at 13.16 W kg⁻¹, and 70% capacitance retention after 1,500 cycles. The improvement originates from the synergistic effects between the double-layer capacitance of GNPLs and the pseudocapacitance of PPy, enabling efficient charge storage and superior cycling durability. These findings highlight that the dielectric behavior of such nanocomposites is closely linked to their electrochemical response, providing valuable insight for designing next-generation polymer-carbon hybrid electrodes. Moreover, the facile, scalable synthesis and mechanical stability of these materials support the development of cost-effective, flexible, and high-energy-density supercapacitors. This aligns with the SDGs by promoting energy technologies that are affordable, reliable, and adaptable to future smart-grid and portable-electronics applications. Conclusively, the GNPLs/PPy system not only demonstrates promising material performance but also holds the potential to accelerate the transition toward cleaner and more resilient energy infrastructures as envisioned in the SDGs.

Limitations of the study

Due to instrument accessibility limitations, additional characterizations such as Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS) could not be performed within the scope of this study. These analyses will be considered in future investigations. The electrochemical measurements in the current study were conducted in a three-electrode system to explore the intrinsic material properties; future work will be focused on two-electrode device fabrication to evaluate practical performance.

Resource availability

Lead contact

Further information and requests for resources and materials should be directed to and will be fulfilled by the lead contact, Dr. Hamsa Noreen (hamsa.noreen@df.unipi.it; hamsaics@yahoo.com).

Materials availability

This study did not generate new unique reagents. The synthesized GNPLs/PPy nanocomposites described in this study are available from the lead contact upon reasonable request.

Data and code availability

• •The data supporting the findings of this study are available from the corresponding author upon reasonable request.
• •This study did not generate custom code or software.
• •Any additional information required to reanalyze the data reported in this paper is available from the lead contact upon request.

Acknowledgments

The author acknowledges the TWAS_CNPq Postgraduate Fellowship (Sandwich PhD Program) (grant no. 315724/2018-8) for financial support during the course of this research. The author also thanks the Department of Physics, University of Pisa, for providing research facilities and institutional support for the publication of this work.

Author contributions

Conceptualization, writing – review and editing, data curation, and validation, G.R.; writing – review and editing, A.-u.-R.; supervision and writing – review and editing, M.Y.; conceptualization, J.I.; supervision, data analysis, and validation, W.H.; validation, R.K.; validation and writing – review and editing, H.N. All authors have read and agreed to the published version of the manuscript.

Declaration of interests

The authors declare no conflict of interest.

STAR★Methods

Key resources table

REAGENT or RESOURCE	SOURCE	IDENTIFIER
Chemicals
Graphene nanoplatelets (GNPLs)	Sigma-Aldrich	7782-42-5
Pyrrole	Sigma-Aldrich	109-97-7
Ferric chloride hexahydrate (FeCl3·6H2O)	Sigma-Aldrich	10025-77-1
Polyvinyl alcohol (PVA)	Alfa Aesar	Product grade
Poly(vinylidene fluoride) (PVDF)	Sigma-Aldrich	24937-79-9
Ethanol	Sigma-Aldrich	64-17-5
Sulfuric acid (H2SO4)	Sigma-Aldrich	7664-93-9
Deionized water	Milli-Q system	Resistivity 18.2 MΩ cm at 25 °C
Software and algorithms
OriginLab	OriginLab Corporation	OriginPro 2024b https://www.originlab.com
Adobe Illustrator	Adobe Systems	Adobe Illustrator 2024 — https://www.adobe.com/products/illustrator.html
Other
Fourier transform infrared spectrometer	PerkinElmer	Spectrum 2
X-ray diffractometer	JEOL	JDX-3532
Scanning electron microscope with EDX	JEOL	JSM-5910
Electrochemical workstation	Gamry Instruments	Interface 1010B – https://www.gamry.com/potentiostats/interface-1010b/

Experimental model and study participant details

This study did not involve human participants, animal subjects, or experimental biological models.

Method details

Chemicals

Graphene nanoplatelets (99.9%, K Nano), Pyrrole (Sigma Aldrich), polyvinyl alcohol (Alfa Aesar) and ferric chloride hexahydrate (FeCl3⋅6H2O, 98%, Sigma Aldrich) have been utilized as collected without any more distillation. Deionized water served as the reaction medium throughout the experiments.

Polypyrrole nanoparticles synthesis

Pristine Polypyrrole nanoparticles were prepared via chemical polymerization process of pyrrole monomer with FeCl₃-PVA mixture solution. Briefly, PVA (1.50 g) solution was stirred at 60°C for 20 min. After that, FeCl₃·6H₂O (1.24 g) was added to the polyvinyl alcohol (PVA) solution, which acts as a stabilizing agent during the oxidative polymerization process and gives orange color mixture. The polymerization was started after 1 h by adding the pyrrole unit into the FeCl₃-PVA mixture. Subsequently, the mixture solution turned into black color and the stirring was preceded for 4 h to complete the process of polymerization. Finally, the produced PPy nanoparticles were centrifuged (4000 rpm). The as-prepared nanomaterials were further washed with distilled water, and then the PPy NPs were then lastly sonicated in the deionized water.

GNPLs and polypyrrole nanocomposites preparation

The GNPLs/PPy nanocomposites were synthesized through an in situ chemical polymerization technique. Mechanistically, different ratios (10–50%) of GNPLs were ultra-sonicated for 25 min. After sonication, monomer pyrrole was mixed with the each percent weight of GNPLs and stirred for 1h. Additionally, three different aqueous solutions of FeCl₃⋅6H₂O (15.5 g) and PVA (1.74 g) were mixed with each GNPLs/PPy weight solutions and kept on stirring for 4 h to establish the polymerization reaction. Finally, the black powder of GNPLs/PPy nanocomposites was centrifuged and wiped with ethanol and then with deionized water, and then the as-prepared nanocomposites were dried at 60°C in a vacuum oven for 24 h.

Preparation of working electrodes

The working electrodes were fabricated by mixing the active material (GNPLs/PPy or pristine PPy) with 5 wt % polyvinylidene fluoride (PVDF) as a binder. The mixture was dispersed in ethanol to form a homogeneous slurry and subsequently drop-cast onto a silver current collector (1 cm²). The coated electrodes were dried at 60 °C to remove residual solvent. The low binder content was selected to provide sufficient mechanical adhesion and film integrity during electrochemical cycling while preserving the intrinsic conductivity and charge-storage behavior of the GNPLs/PPy composite. No additional conductive additive was used, as the interconnected graphene nanoplatelet network and conductive PPy matrix ensure efficient electron transport.

Structural characterization

The Fourier transform infrared spectra (PerkinElmer Spectrum 2), X-ray powder diffraction (XRD) (JDX-3532, JEOL), SEM and EDX (JSM-5910, JEOL) were performed for the assessment of band formations, phase, composition and surface topography of the electrodes. FTIR spectra were recorded using ATR mode, which enables direct analysis of polymer nanocomposites without additional sample preparation.

Dielectric properties

The dielectric behavior of Pristine PPy NPs and GNPLs/PPy (10–50%) nanocomposites were estimated over a wide range of frequencies i.e., 50 Hz to 20 MHz at optimum temperature with difference of imaginary and real complex parts, dielectric permittivity and dielectric loss tangent (tan δ, where tan δ = ε′′/ε′) by modeling the nanocomposites in pellets form.

Electrochemical measurements

The electrochemical measurements were performed by GCD, EIS and CV using a GAMRAY Interface 1010B in 1M H₂SO₄ aqueous electrolyte. H₂SO₄ was used as an electrolyte because of its high ionic conductivity and favorable interaction with conducting polymers which enables the effective redox activity. The electrochemical cell consisted of three electrodes mode with a 1 cm silver plate working electrode, Pt plate counter electrode, and saturated calomel electrode (SCE) reference electrode as shown in Figures 6A and 6B. A saturated calomel electrode (SCE) was used as a reference electrode due to stable and reproducible potential in acidic aqueous electrolytes. The CV detection was completed at scan rates of 10, 30, 50, 70, 100, 150 and 200 mV s⁻¹ in range of −0.2 to 1 V potential window. EIS study was evaluated with amplitude of 5 mV in 20 kHz-0.1 Hz frequency at open-circuit voltage. The charge-discharge (GCDs) plot was estimated at different current densities i.e., 0.25–10 A/g.

Quantification and statistical analysis

Electrochemical data were analyzed using OriginPro 2024b software. Specific capacitance values were calculated from cyclic voltammetry and galvanostatic charge–discharge measurements using standard electrochemical equations. All measurements were performed under identical experimental conditions to ensure reliable comparison among different GNPLs loading compositions.